Paste-bond clevis joint

ABSTRACT

A method is provided for using a three-dimensional, Pi-shaped, woven preform to assemble first and second composite components. The preform is infused with resin, and at least one surface of the preform is adhered to at least one surface of the first component using a film adhesive. The preform is cured while an oversized tool coated with non-stick material is located within a clevis formed by two legs of the preform. A removable peel ply is located between the tool and the clevis, and semi-rigid over-presses are used during curing. After curing, the tool, over-presses, and peel ply are removed, and adhesive is injected into the clevis. The second component is inserted into the clevis, the adhesive adhering to an inner surface of the clevis and to at least one surface of the second component for retaining the second component within the clevis, the second component having a smaller width than the tool.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention generally relates to assembly of components using wovenpreforms and particularly relates to assembly using a paste adhesivewithin a clevis of a cured preform.

2. Description of the Prior Art

Typical methods known in the art for attaching a composite skin to acomposite web include forming the web as an “I” or “C” shape, makingthem more complex and expensive to fabricate. The flanged sections arefastened to adjacent sections using methods similar to those used withmetal components, for example, by using fasteners. However, use of thefasteners adds weight and cost to the joints.

Also, these joints have difficulty withstanding out-of-plane loading.Typical remedies for this are thick laminate stack-ups using many layersof composite fabric and having large flange radii. While this reducesthe tensions forces between the layers of the flanged section, theresult is a heavy joint, reducing the weight savings realized when usingcomposites.

SUMMARY OF THE INVENTION

A woven preform transfers out-of-plane loading through directed fibersto minimize inter-laminar tension. The preform is cured in position onthe skin, the web being inserted during final assembly into a clevisformed by the preform. Composite substructure components can befabricated having flat, bladed webs, which reduces complexity and costof fabrication. The result is an efficient way to assemble compositeparts without the use of fasteners or flanged sections.

A method is provided for using a three-dimensional, Pi-shaped, wovenpreform to assemble first and second composite components. The preformis infused with resin, and at least one surface of the preform isadhered to at least one surface of the first component using a filmadhesive. The preform is cured while an oversized tool coated withnon-stick material is located within a clevis formed by two legs of thepreform. A removable peel ply is located between the tool and theclevis, and semi-rigid over-presses are used during curing to distributeinwardly-directed forces across the preform. After curing, the tool,over-presses, and peel ply are removed, and adhesive is injected intothe clevis. The second component is inserted into the clevis, theadhesive adhering to an inner surface of the clevis and to at least onesurface of the second component for retaining the second componentwithin the clevis, the second component having a smaller width than thetool.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features believed to be characteristic of the invention areset forth in the appended claims. The invention itself however, as wellas a preferred mode of use, further objects and advantages thereof, willbest be understood by reference to the following detailed description ofan illustrative embodiment when read in conjunction with theaccompanying drawings, wherein:

FIG. 1 is a perspective view of an assembly using a preform and inaccordance with the present invention; and

FIG. 2 is a front view of the preform of FIG. 1 after installation.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1 and 2 show a pi-shaped, 3-D, woven preform 11 used to connecttwo composite parts 13, 15, which may be, for example, a frame member 13and a skin 15, or other member. Preform 11, frame 13, and skin 15 areinfused with a resin, for example, 977-3, available from CytecIndustries, Inc. of West Paterson, N.J. Preform 11 is not cured prior toassembly. Frame 13 is cured prior to assembly, and skin 15 may be curedprior to preform 11 being adhered to skin 15. Alternatively, skin 15 andpreform 11 may be co-cured as an assembly. Preform 11 may be woven frommaterials such as carbon fibers, Kevlar fibers, glass fibers, or othermaterials, or may be a combination of material types.

As shown in the figures, preform 11 has a base 17 on its lower portionthat has a continuous, flat lower surface 19. A pair of spaced-apartplanar legs 21 extend vertically upward from base 17, forming a clevis20, or slot. Each leg 21 is at a position that is offset from, but nearto, the center of base 17. Legs 21 are shown as parallel to each otherand perpendicular to base 17, though legs 21 could be at angles to eachother and to base 17. Legs 21 could be oriented to be farther apart atthe top of legs 21, forming a “V” shape. In the installed positionshown, inner surfaces 23 of legs 21 face each other for receiving framemember 13. A small, upward-facing surface 25 of base 17 lies between thelower ends of legs 21. Though it is preferable for the outer surface oflegs 21 and the upper surface of base 17 to be tapered at their outerends, as shown, the ends may also be squared.

FIG. 1 is an exploded view of the components used to form the desiredshape when curing preform 11. Here, skin 15 has been cured prior toassembly. An adhesive film 27, for example, AF191, available from 3M ofSt. Paul, Minn., is placed between lower surface 19 of preform 11 andupper surface 29 of skin 15 for adhering preform 11 to skin 15.

Various resin systems are sold under the terms “laminating resins” and“adhesives,” though there is no “bright-line,”industry-standarddefinition by which to distinguish one from the other. The term“adhesive” is used herein to mean a resin system that has a lowermodulus of elasticity and/or a higher strain-to-failure than the resinforming the matrix of the parts to be adhered. The combination of thesecharacteristics is described as higher toughness, and adhesives have ahigher toughness than laminating resins, which tend to be more brittleand have lower crack-formation loads.

Results from ASTM tests can be used to distinguish, generally, betweenlaminating resins and adhesives. High-strength, structural laminatingresins have a peel strength rating generally ranging from 0-15 poundsper linear inch, whereas the peel strength of adhesives are greater than15 pounds per linear inch. For example, the Bell Peel test (ASTM D3167“Standard Test Method for Floating Roller Peel Resistance of Adhesives”)shows that the peel strength of AF191 is 30-45 pounds per linear inch atroom temperature, but the peel strength of 977-3, which is used tolaminate the parts, is 0-6 pounds per linear inch. In addition,laminating resins generally have a tensile strength greater than 7500pounds per square inch (psi) as tested using ASTM D638 (“Standard TestMethod for Tensile Properties of Plastics”), with high-strength resinsranging to 10000 psi. Adhesives generally have tensile strengths leesthan 6500 psi. Thus, in the present application, “adhesives” also meansresin systems with tensile strengths less than 6500 psi and a peelstrength greater than 15 pounds per linear inch. “Laminating resins” isused to mean resin systems having tensile strengths greater than 7500psi and a peel strength of less than 15 pounds per linear inch.

A resin-infused textile layer forms an over-wrap ply 31 and is laid onthe outer surface of each leg 21 and on the outer ends of the uppersurface of base 17, over-wrap ply 31 extending beyond the outer ends ofbase 17. Over-wrap ply 31 provides an additional connective layerbetween preform 11 and skin 15. Adhesive film 27 extends to or beyondthe outermost edge of the lower portions of over-wrap plies 31. Eachover-wrap ply 31 extends upward to the upper edge of leg 21. A peel ply33, a fabric layer preferably made from Kevlar, is inserted between legs21, peel ply 33 clinging to uncured resin on inner surfaces 23 of legs21. Peel ply 33 is removed prior to assembly with frame 13 (FIG. 2),ensuring a clean bonding surface within clevis 20. Peel ply 33 allowsfor easier removal of shaping tool 35 after curing of preform 11.

Tool 35 is shown as planar and having a rectangular cross-section sizedto have a larger lateral width than that of frame 13, though tool 35 canalso be tapered when necessary for the desired shape. The oversizewidth, preferably 0.002″ to 0.120″ wider than frame 13, provides for agap or clearance between frame 13 and inner surfaces 23 of legs 21 whenframe 13 is inserted into clevis 20. Tool 35 is coated with Teflon onsurfaces 37, 39 to ensure a minimum of force is necessary to remove tool35 after curing of preform 11. Surfaces 37, 39 contact peel ply 33 andshape the volume between legs 21. Semi-rigid over-presses 41 are used todistribute force applied to over-presses 41 across the width and heightof preform 11, surfaces 43, 45 being in contact with over-wrap plies 31.Each over-press 41 is generally triangular in cross-section. Thedistribution of force causes more consistent bonding at the interface ofskin 15 and preform 11 and a more consistent shaping of clevis 20 to theshape of tool 35.

To assemble skin 15 and frame 13, preform 11 is infused with resin, andadhesive film 27 is placed on upper surface 29 of skin 15. Adhesive film27 and preform 11 are tacky, the resin remaining in preform 11. Lowersurface 19 of preform 11 is placed against adhesive film 27 in thedesired position. Adhesive film 27 forms a bonding layer at theinterface of lower surface 19 of preform 11 and upper surface 29 of skin15. Over-wrap plies 31 are infused with resin and laid on the outersurfaces of base 17 and legs 21, the over-wrap plies 31 extending upwardto the edges of legs 21 and laterally outward beyond the outer edges ofbase 17. Adhesive film 27 extends to or beyond the outer edge of eachover-wrap ply 31 and bonds the outer portion of plies 31 to skin 15.

A peel ply 33 is inserted between legs 21, the peel ply 33 clinging tothe uncured resin on inner surfaces 23 of legs 21 and on surface 25,surfaces 23, 25 forming the inside of clevis 20. Oversized tool 35,which is coated with a non-stick material, is inserted into clevis 20and over-presses 39 are placed against the over-wrap plies 31. Theassembly and tooling are placed within a vacuum bag (not shown) fromwhich the air is drawn, allowing outside air pressure to apply force toover-presses 39. This forces base 17 toward skin 15 and forces legs 21toward tool 35, causing preform 11 to take the desired shape. Theassembly is preferably placed into an oven to cure preform 11 andadhesive film 27 concurrently, adhering preform 11 to skin 15.

Referring to FIG. 2, after curing, vacuum bag and over-presses 41 areremoved. Tool 35 is removed from clevis 20, and peel ply 33 is peeledfrom inner surfaces 23 and surface 25. An adhesive 47 that is preferablyin a paste form, for example, Hysol® EA 9394, available from DexterAdhesive Systems of Bay Point, Calif., is injected into clevis 20, andthe outer surfaces 49, 51 of frame are wetted with additional adhesive47. EA 9394 has a maximum peel strength of 20 pounds per linear inch,placing it in the range of the adhesives. Adhesive 47 is thickened intoa paste form by adding a thickening agent, causing adhesive 47 to have ahigh enough viscosity to prevent adhesive 47 from flowing out of clevis20 even when preform 11 is turned upside down. Frame 13 is inserted intoclevis 20, adhesive 47 filling the gap between inner surfaces 23 of legs21 and surfaces 49 of frame 13 and between surface 25 of preform 11 andsurface 51 of frame 13. Since the amount of oversizing of tool 35determines the amount and thickness of adhesive 47 remaining betweenframe 13 and inner surfaces 23 after insertion of frame 13, the width oftool 35 will be determined from the assembly tolerance requirements andby the strength required in the joint. Mechanical pressure is applied tomaintain the proper positioning of parts 13, 15, and adhesive 47 iscured to form a bonding layer between cured preform 11 and frame 13.Though EA 9394 cures at room temperature, local heat can be applied whennecessary to cure the paste adhesive used. FIG. 2 shows a completedassembly, frame 13 being secured to skin 15.

The advantages of the present invention include the ability to form anassembly of composite components using a clevis joint and without usingfasteners. By forming the clevis with a three-dimensional woven preform,the need for fasteners is eliminated. Also, the method provides for ameans of installing a composite closeout panel or other component whenthe backside of the joint is not accessible for vacuum-bagging. Forexample, the present invention is useful in creating wing structures intwo halves and then bonding the halves, the devises being on one half ofthe wing structure, the frame webs being on the other half.

While the invention has been shown in only some of its forms, it is notthus limited but is susceptible to various changes and modificationswithout departing from the spirit thereof.

1. A method for assembling first and second composite components, themethod comprising: (a) providing a woven preform having a base and apair of spaced-apart legs extending from the base; (b) infusing thepreform with resin, and adhering the base of the preform to the firstcomponent; (c) inserting a sizing tool between the legs and curing theresin while the tool is located between the legs to define a slot; and(d) removing the tool and applying an adhesive into the slot; then (e)inserting the second component into the slot, the adhesive in the slotadhering at least one surface of the second component to at least oneinner surface of the slot for retaining the second component within theslot, the second component having a smaller width than the tool.
 2. Themethod of claim 1, wherein: step (b) further comprises locating a filmadhesive between the base of the preform and the first component.
 3. Themethod of claim 1, wherein: step (c) further comprises locating a peelply within the slot, the peel ply separating the tool and the preformand being removable from the slot after the tool is removed.
 4. Themethod of claim 1, further comprising: coating the tool with a non-stickmaterial to prevent adhesion of the tool to the legs and to reduce theforce needed to remove the tool after curing of the preform.
 5. Themethod of claim 1, wherein: step (c) further comprises placingsemi-rigid over-presses against outer surfaces of the base and the legsof the preform and placing the first component, the preform, theover-presses and the tool within a vacuum bag while curing the preform,each of the over-presses being generally triangular in cross-section fordistributing a force across the preform.
 6. The method of claim 1,further comprising: adhering an over-wrap ply to the preform.
 7. Themethod of claim 1, wherein: steps (c) further comprises forming the legsto be perpendicular to the base.
 8. The method of claim 1, wherein:steps (c) further comprises forming the legs to be parallel to eachother.
 9. The method of claim 1, wherein: step (c) further comprisesvacuum bagging the first components and preform to ensure proper sizingand bonding.
 10. The method of claim 1, wherein: the tool has a greaterwidth than the second component, providing a clearance for the adhesivein the slot.
 11. The method of claim 1, wherein: step (d) furthercomprises coating inside surfaces of the legs with the adhesive.
 12. Amethod for assembling first and second composite components, the methodcomprising: (a) providing a three-dimensional, woven preform having abase and a pair of spaced-apart, generally-parallel legs extending fromthe base; then (b) infusing the preform with resin, and adhering atleast one surface of the preform to at least one surface of the firstcomponent using a film adhesive; then (c) inserting a sizing toolbetween the legs and curing the resin and film adhesive while the toolis located between the legs to define a slot and bond the preform to thefirst component; then (d) removing the tool and applying a pasteadhesive into the slot, the paste adhesive coating inside surfaces ofthe legs; and (e) inserting the second component into the slot, thepaste adhesive adhering at least one surface of the second component toat least one inner surface of the slot for retaining the secondcomponent within the slot, the second component having a smaller widththan the tool.
 13. The method of claim 12, further comprising: step (c)comprises locating a peel ply within the slot, the peel ply beingbetween the tool and the preform and being removable from the slot afterthe tool is removed.
 14. The method of claim 12, further comprising:coating the tool with a non-stick material to reduce the force needed toremove the tool after curing of the preform.
 15. The method of claim 12,wherein: step (c) further comprises placing semi-rigid over-pressesagainst outer surfaces of the base and the legs of the preform andplacing the preform, the first component, the tool and the over-presseswithin a vacuum bag while curing the preform, the over-presses beinggenerally triangular in cross-section for distributing a force acrossthe preform.
 16. The method of claim 12, further comprising: adhering anover-wrap ply to the preform and to the adhesive film.
 17. The method ofclaim 12, wherein: step (c) further comprises vacuum bagging the firstcomponents and preform to ensure proper sizing and bonding.
 18. A methodfor assembling first and second composite components, the methodcomprising: (a) providing a three-dimensional, woven preform having abase and a pair of spaced-apart parallel legs extending from the base;(b) infusing the preform with resin, and adhering the base of thepreform to at least one surface of the first component using a filmadhesive, the first component being a composite member that ispre-cured; (c) inserting a peel ply between the legs and inserting atool within the peel ply between the legs; then (d) placing semi-rigidover-presses against outer surfaces of the base and the legs of thepreform and placing the first component, the preform, the over-pressesand the tool within a vacuum bag and curing the resin and film adhesivewhile the tool is located between the legs to define a clevis and bondthe preform to the first component, the legs being perpendicular to thebase; then (e) removing the tool, removing the peel ply, and applying apaste adhesive into the clevis; and (f) inserting the second componentinto the clevis, the second component being a composite member that ispre-cured, the paste adhesive adhering at least one surface of thesecond component to at least one inner surface of the clevis forretaining the second component within the clevis, the second componenthaving a smaller width than the tool.